Gd-DTPA bolus tracking in the myocardium using T-1 fast acquisition relaxation mapping (T-1 FARM)

MRI methods currently used for bolus tracking in the myocardium, such as sa turation recovery turbo-fast low-angle shot (FLASH) (srTFL), are limited by signal intensity (SI) saturation at high contrast agent (CA) concentration s. By using T-1 fast acquisition relaxation mapping (T-1 FARM), a Gd-DTPA b olus (0.075 vs. 0.025 mmol/kg) may be injected without causing saturation. This study tested the feasibility of in vivo T-1 FARM bolus tracking under rest/stress conditions in seven beagles with multiple permanently occluded branches of the left anterior descending (LAD) coronary artery. Although it underestimated the myocardial perfusion reserve (MPR) measured ex vivo usi ng radioactive microspheres (mean SEM; 3.60 +/- 0.26), the MPR determined u pon application of the modified Kety model (1.86 +/- 0.10) enabled distinct ion between normal and infarcted tissue. The partition coefficient (lambda) estimated at rest and stress using the modified Kety model underestimated ex vivo radioactive measurements in infarcted tissue (0.25 +/- 0.01 vs. 0.2 6 +/- 0.01 vs. 0.79 +/- 0.08 ml/g, P < 0.0001) yet was accurate in normal t issue (0.28 +/- 0.01 vs. 0.30 +/- 0.01 vs. 0.33 +/- 0.01 ml/g, P = NS). Thu s, although unsuitable far myocardial viability assessment, Ti FARM bolus t racking shows potential for assessment of myocardial perfusion.